I have a client (I'm an IT consultant) that is building out a new office - they are a medical practice that is expanding, and so one of the things we are going to be doing is setting up a dedicated network closet with a rack for their server(s), etc. They are going to have a lot of stuff in there (several servers, network equipment, phone system, sound system, lighting system, etc.), and so my concern is getting the appropriate electrical in that closet.

I am not an electrician, and don't usually deal with electrical matters beyond UPS's (which they will also have), but I recall the electrician stating they were going to be putting a good amount of outlets in there as well as a dedicated circuit (or something similar - can't recall his exact words). When I went to look just now (it's mostly finished), all I see was one grouping of four outlets (similar to this, although not sure if they were 15-amp or 20-amp: https://image.shutterstock.com/z/stock-photo-a-plex-electrical-outlet-for-volts-in-north-america-165.... To me, that seems like not nearly enough, and it would seem we'd probably want to make sure that whatever outlets were in the network closet were dedicated (or whatever the correct terminology is for that).

Am I off-base here? Can anyone shed some light on this for me so I can go back to the client, the contractor, and the electrician to get things squared away? Thanks!

From the linked diagram, the only mention of 'cooling' I see is the mention of an 'Exhaust Fan' that is controlled by a switch. An exhaust fan will not likely be able to provide enough cool air, especially if someone turns off its switch. HVAC requirements seriously need to be reviewed and deficiencies addressed.

From the linked diagram, the only mention of 'cooling' I see is the mention of an 'Exhaust Fan' that is controlled by a switch. An exhaust fan will not likely be able to provide enough cool air, especially if someone turns off its switch. HVAC requirements seriously need to be reviewed and deficiencies addressed.

I agree the cooling requirements need to be evaluated, but I would think twice before installing a dedicated AC unit for a small closet.

Modern equipment is much more thermally efficient than in previous years, and is generally fine even in quite warm conditions. A typical modern server is rated for continual operation at temperatures up to 100°F.

Hopefully this will be a virtualized environment, so the actual number of physical servers will be small, and switches and audio equipment generally don't require the same level of cooling as servers.

An exhaust fan may be perfectly adequate as long as it's big enough and positioned appropriately. The cooler air coming in needs to flow across the
front of the equipment, and the warmer air needs to be pulled from the
back. If cool air is coming from the gap under the closet door, the vent
fan should be at the back of the closet near the ceiling to ensure the air flows through the equipment and carries the heat out the exhaust.

The biggest risks are actually from rapid changes in temperature. You're better off operating at 90°
all the time, than operating at 65° most of the time, then suddenly shooting up to 120 during a power failure.

Dedicated AC for a server closet also means additional wiring, plumbing for drainage, and additional maintenance and repair concerns.

What happens when it fails? How quickly can it be repaired? What happens if the drain gets clogged and it overflows? Where's that water going?

ACs are more likely to fail and more difficult to repair when they do fail than simple fans, and keeping an AC running during a power failure also dramatically increases the UPS requirements.

Speaking from extensive personal experience with dedicated server AC, I have found it to be a bigger source of problems than actual heat.

54 Replies

If we assume that the single two-gang box with four receptacles in it is on a single ("dedicated") circuit and the outlets have two vertical slots, it's 15A. If they have one slot that looks like a T, then it's 20A.

Any UPS you buy with a two-vertical slot plug is going to handle a maximum of 15A.

You can plug four devices into your outlets, but you're only going to get a total of 15A total before the breaker trips.

If we assume that the single two-gang box with four receptacles in it is on a single ("dedicated") circuit and the outlets have two vertical slots, it's 15A. If they have one slot that looks like a T, then it's 20A.

Any UPS you buy with a two-vertical slot plug is going to handle a maximum of 15A.

You can plug four devices into your outlets, but you're only going to get a total of 15A total before the breaker trips.

Multiple servers, UPSes, sound systems, etc. You'll want at least two independent circuits, but only because you need more than 15A.

Do the power budget.

As mentioned, I'm not an electrician, and this is mostly beyond the scope of the work I provide to this client. But, as mentioned, we are going to have multiple servers, UPS's, sound system, etc., so it sounds like what is currently in there is insufficient.

So it sounds like right now we either have one independent 15A or 20A circuit, right? I would think we'd want at least 2, maybe more though?

It sounds like you need to get the electrician in there and ask him to tell you exactly what is installed. If your running two UPSs definitely you need at least 2 separate circuits. Just as Robert5205​ stated, figure out what you need for power, or your Power Budget as he stated.

Here's what I was just able to get off the electrical drawing. Can anyone translate/explain? Thanks!

You may really want to ask what those symbol means.....to me it looks like 25 & 45 outlets or face-plates.

...

I would say the UPS is one main point where IT consultants meet Electricians...you need to do the power spec of the UPS required (that requires to know what hardware will be installed) then do the count for 2nd power supply either to PDUs or directly to the wall.

As Robert notes, you're probably fine with a standard wall socket. If you want to be absolutely sure, total up the power consumption of everything that's going to need power in the closet. As long as you're 1500 VA or below, you're fine. If you go over, you'll likely need a 20A or 30A wall socket so you can plug in the UPS (from there, everything plugs into the UPS though things like a maintenance bypass can help you increase reliability and reduce downtime https://www.eaton.com/us/en-us/products/backup-power-ups-surge-it-power-distribution/backup-power-up...).

Okay, I don't know what the hell is wrong with Mike, but that's funny stuff! HA!

Seriously, though, don't mess around with (or ignore!) power factors. I second the idea of having an actual conversation with the electrician. Make sure you understand the terms s/he uses, too. Whatever you do, make sure you aren't setting up your client for future problems with this closet. Last point, timing is pretty important; it's better to get all this worked out while construction is still happening than afterwards.

The initial Shutter Shock image you posted is for a bank of 4 NEMA 5-20R, the "5" implies 120 volts AC and the 20 implies a max of 20 amps. The breaker feeding the circuit may or may not be dedicated, so input from the electrician will be useful.

Do you already have an equipment list of the devices that need to be plugged in? Feel free to post it or shoot me a direct message. That will be what drives how much amperage a given circuit needs to be. If there are PoE devices, be sure to take those into account. Understanding the basics of UPS sizing we cover here would help if you're going to have a call with an electrician.

To Kenneth2823​ 's point, cooling will be important. Remember that more wattage consumed by electrical equipment in the room will mean more BTUs needed from your cooling system. If a spot cooler or in-rack air-conditioner could help, check out this article.

From the linked diagram, the only mention of 'cooling' I see is the mention of an 'Exhaust Fan' that is controlled by a switch. An exhaust fan will not likely be able to provide enough cool air, especially if someone turns off its switch. HVAC requirements seriously need to be reviewed and deficiencies addressed.

I'll add this. If you plan to have multiple servers with dual power supplies, then double your UPS's too. Which means you will at the minimum want 2 dedicated 20amp circuits. Which based on what you've told us and shown in the diagram you only have one. So one UPS on one dedicated circuit. Then have an 'A' and a 'B' PDUs. PDU A goes to UPS1 and PDU B goes to UPS2. Server power supply 1 goes to PDU A and power supply 2 goes to PDU B. This way if you shut down one of the UPSs the servers stay up and running as the 2nd power supplies are still getting power from the 2nd UPS. For items with only 1 power supply I use an Eaton pdu that takes 2 power sources.

But like the others have said, we really don't know your total power requirements. But I'd like to think you would be fine with just 2 dedicated 20amps.

From the linked diagram, the only mention of 'cooling' I see is the mention of an 'Exhaust Fan' that is controlled by a switch. An exhaust fan will not likely be able to provide enough cool air, especially if someone turns off its switch. HVAC requirements seriously need to be reviewed and deficiencies addressed.

I agree the cooling requirements need to be evaluated, but I would think twice before installing a dedicated AC unit for a small closet.

Modern equipment is much more thermally efficient than in previous years, and is generally fine even in quite warm conditions. A typical modern server is rated for continual operation at temperatures up to 100°F.

Hopefully this will be a virtualized environment, so the actual number of physical servers will be small, and switches and audio equipment generally don't require the same level of cooling as servers.

An exhaust fan may be perfectly adequate as long as it's big enough and positioned appropriately. The cooler air coming in needs to flow across the
front of the equipment, and the warmer air needs to be pulled from the
back. If cool air is coming from the gap under the closet door, the vent
fan should be at the back of the closet near the ceiling to ensure the air flows through the equipment and carries the heat out the exhaust.

The biggest risks are actually from rapid changes in temperature. You're better off operating at 90°
all the time, than operating at 65° most of the time, then suddenly shooting up to 120 during a power failure.

Dedicated AC for a server closet also means additional wiring, plumbing for drainage, and additional maintenance and repair concerns.

What happens when it fails? How quickly can it be repaired? What happens if the drain gets clogged and it overflows? Where's that water going?

ACs are more likely to fail and more difficult to repair when they do fail than simple fans, and keeping an AC running during a power failure also dramatically increases the UPS requirements.

Speaking from extensive personal experience with dedicated server AC, I have found it to be a bigger source of problems than actual heat.

I agree the cooling requirements need to be evaluated, but I would think twice before installing a dedicated AC unit for a small closet.

Modern equipment is much more thermally efficient than in previous years, and is generally fine even in quite warm conditions. A typical modern server is rated for continual operation at temperatures up to 100°F.

One related point to consider: SLA (sealed lead acid) batteries found in a lot of UPSes today would be an exception to this. As a rule of thumb, for every 15 degrees F above 77 F, you can cut expected battery life in half. Lithium is changing things a bit, but SLA is still the norm today. We talk about SLA battery life in more detail in this Spiceworks thread.

I agree the cooling requirements need to be evaluated, but I would think twice before installing a dedicated AC unit for a small closet.

Modern equipment is much more thermally efficient than in previous years, and is generally fine even in quite warm conditions. A typical modern server is rated for continual operation at temperatures up to 100°F.

One related point to consider: SLA (sealed lead acid) batteries found in a lot of UPSes today would be an exception to this. As a rule of thumb, for every 15 degrees F above 77 F, you can cut expected battery life in half. Lithium is changing things a bit, but SLA is still the norm today. We talk about SLA battery life in more detail in this Spiceworks thread.

A good point, but in my case, the UPSes are mounted very low due to their weight, and I suspect most people do the same. Having air exhaust through the ceiling ensures the batteries are actually in the coolest part of the room.

All of us can give lots of advice on electrical, equipment, cooling and calculations. My question would be - does your Consulting contract leave you holding the bag if something is done wrong?

A suggestion - find someone you trust, who does understand all of this, and have that person serve as your Consultant in reviewing this and, if needed, requesting changes in writing. CYA. Architects and contractors don't always get IT done correctly. I've been through construction a few times.

Not an electrician but know a fair bit. It is possible to have each outlet in a 4 outlet box connected to an independent breaker, so four breakers at 15 amp each or in the case of the image 4 outlets at 20 amps each.

In a kitchen in North America, the top outlet and bottom outlet of a duplex outlet, are usually on different breakers.

David provides the best information. I keep going back to that diagram, and would have to see the whole thing to get some other examples. The big thing is the numbers. They're giving you the four plugs in the room. '24' and '45' confuse me because why would they list numbers so far apart for the same room, for either jacks or breakers? In my case, I specifically asked for two separate circuits to my main room. The electricians gave me one, with four plugs. *Sigh* Yours will probably do the same, so you'd better go talk to them quickly if you want to make changes.

To give you an idea, from those four plugs I run a 12,000 BTU air conditioner and three UPS units (2x 1500VA and 1x 1000VA). Those feed 2x POE 24-port switches (under-utilized), 2x servers and an 8 port (half-filled) NAS.

So you're going to have that, PLUS an additional circuit for your 'Server', as they term it.

A lot of really good information presented here. I went through it 12 yrs ago and didn't have a resource like Spiceworks to turn to.The electrician and the building owners (under advisement by the electrician) were going to do something similar for me like what you're presented with. I had one four gang wall outlet going to two 20 amp breakers.

Fortunately I understood about load requirements and to override a smart-aleck electrician I took copies of the load requirements of just the servers we had at the time and showed them to the building owners, also told them that wasn't the only equipment we were going to be running in there. That got me 3 more circuits and several more outlets around the room.

Unfortunately they wouldn't listen about the A/C requirements and the first day we fired everything up it quickly heated up to 95 degrees in there, by mid-day we were running between 100 and 105 degrees with the door open and a fan positioned in the doorway. Turning the fan around to exhaust the heat rather than trying to blow cooler air dropped it back to 95 degrees.

As a full service IT Consultant electrical requirements are something you SHOULD know and be familiar with. Power issues can be a REAL problem, and a REAL BIG HEADACHE that you will never be able to troubleshoot without some knowledge. You don't need to know how to wire, but you do need to understand volts, amperes, watts, Volt-Amps, and BTUs (necessary to help determine cooling requirements). You should also carry a power line tester, nothing fancy, but something that will tell you if an outlet is wired correctly or not.

First of all it's not that hard to calculate. Robert5205 is absolutely correct in that you really need to do the power budget. How many servers, what is the max rating of each power supply, what is the power supply rating of the switches, and each other piece of the electrical that will be in that closet. Is everything running on 110V or is there something that requires 208V? After you have that total number, add about 50%-75% for headroom and the fact that what we see in a 700 watt power supply is the OUTPUT of that supply, not the INPUT, there is loss in conversion form AC to DC, anywhere from 5% to 30% depending on the supply. Remember that number. Next determine the UPS requirements, what equipment must be UPS'ed, I doubt all of it will require that, and you will need at least 2 UPS's, perhaps more depending on if you have 208V equipment.or not. Every UPS should be on it's own dedicated circuit, depending on the size of the UPS's needed that will tell you much about the outlets that will be required. If you need 3000 watt UPS's or larger, those will only be supported with a 30AMP dedicated line, so you might need two of those. There are UPS sizing guides out there to use.

The sound system should have it's own dedicated line, mostly so it has a non-shared neutral and ground to help eliminate hum, it probably won't need to be UPS'ed, but, if it's used for emergency announcements, it should be on one, and it should be separate from the UPS's that you have computing equipment on. Generally a sound system outlet should be as far away from the other systems as practical, just to minimize cross-talk and background hum. Number of outlets is dependent on the number of amplifiers and sound distribution system, but figure a minimum of four.

You will also likely have requirements for phone connections, usually pretty low wattage, and a connection to a UPS is optional, but handy, figure you will need at least two outlets for phone equipment, Next all the fire alarm equipment, add two outlets for that, then the lighting controls, those will likely be hardwired, and not require an outlet, but best add two outlets for them. Then add a coupe more outlets for use with diagnostic equipment if you need to power a laptop or something else. So far I think were up to about 14 outlets, with 7 or so dedicated lines.

Now for cooling, remember that total wattage number from before? Add 15% and that is the amount of heat you can be adding to that room constantly. I suspect that total number will turn out to be somewhere around 1500-2000 watts for a small computer room, and well over 5000 watts for a medium sized room. Essentially that is the same as putting 4 space heaters running at full blast in a room at once. It can be a real problem for a small vent fan to eliminate, especially one that is mislocated. Bill2718 is right in that a modern server can run at almost 100F reliably, but, the fans are going to be screaming while it's doing it. So is the sound insulation good enough to keep the noise level tolerable elsewhere in the office, or would adding cooling (and sometimes just the regular building AC is all that's necessary) keep the temp below 80F, and the fan noise lower. There are conversions for watt's to BTU's but for a small computer room 10,000 BTU's will handle around 2900 watt's of added heat. Adding cooling complicates things, but it needs it's own power, and if you have to you can use one of the 'portable' air conditioners but remember their effective BTU's is about 1/2 of their rated BTU, because the condenser unit is inside the enclosed space, even if vented outside the space. (Also make sure that the unit isn't an 'evaporative' unit, they cool, and are cheaper, but they also add humidity, and you have to add water to them.) If you do install a portable air conditioner add one more dedicated line, and two more outlets for it.

What I've gone over is stuff you should already know, and have calculated for each of your customers just to make sure they are properly supported and have the proper equipment. It's one of the first things I do after changing jobs. It gives me a real handle on exactly what's what, and were things done correctly, and what needs to happen to be properly supported, so that power isn't something that you have to consider when problems arise.